| NETINTRO(4) | Device Drivers Manual | NETINTRO(4) |
networking —
introduction to networking facilities
#include
<sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/route.h>
This section is a general introduction to the networking facilities available in the system. Documentation in this part of section 4 is broken up into three areas: protocol families (domains), protocols, and network interfaces.
All network protocols are associated with a specific protocol family. A protocol family provides basic services to the protocol implementation to allow it to function within a specific network environment. These services may include packet fragmentation and reassembly, routing, addressing, and basic transport. A protocol family may support multiple methods of addressing, though the current protocol implementations do not. A protocol family is normally comprised of a number of protocols, one per socket(2) type. It is not required that a protocol family support all socket types. A protocol family may contain multiple protocols supporting the same socket abstraction.
A protocol supports one of the socket abstractions detailed in
socket(2). A specific protocol may be accessed either by
creating a socket of the appropriate type and protocol family, or by
requesting the protocol explicitly when creating a socket. Protocols
normally accept only one type of address format, usually determined by the
addressing structure inherent in the design of the protocol family/network
architecture. Certain semantics of the basic socket abstractions are
protocol specific. All protocols are expected to support the basic model for
their particular socket type, but may, in addition, provide non-standard
facilities or extensions to a mechanism. For example, a protocol supporting
the SOCK_STREAM abstraction may allow more than one
byte of out-of-band data to be transmitted per out-of-band message.
A network interface is similar to a device interface. Network interfaces comprise the lowest layer of the networking subsystem, interacting with the actual transport hardware. An interface may support one or more protocol families and/or address formats. The SYNOPSIS section of each network interface entry gives a sample specification of the related drivers for use in providing a system description to the config(8) program. The DIAGNOSTICS section lists messages which may appear on the console and/or in the system error log, /var/log/messages (see syslogd(8)), due to errors in device operation.
The system currently supports the Internet protocols, the Xerox Network Systems(tm) protocols, and some of the ISO OSI protocols. Raw socket interfaces are provided to the IP protocol layer of the Internet, and to the IDP protocol of Xerox NS. Consult the appropriate manual pages in this section for more information regarding the support for each protocol family.
Associated with each protocol family is an address format. All network addresses adhere to a general structure, called a sockaddr, described below. However, each protocol imposes finer and more specific structure, generally renaming the variant, which is discussed in the protocol family manual page alluded to above.
struct sockaddr {
u_char sa_len;
u_char sa_family;
char sa_data[14];
};
The field sa_len contains the total length of the structure, which may exceed 16 bytes. The following address values for sa_family are known to the system (and additional formats are defined for possible future implementation):
#define AF_UNIX 1 /* local to host (pipes, portals) */ #define AF_INET 2 /* internetwork: UDP, TCP, etc. */ #define AF_NS 6 /* Xerox NS protocols */ #define AF_CCITT 10 /* CCITT protocols, X.25 etc */ #define AF_HYLINK 15 /* NSC Hyperchannel */ #define AF_ISO 18 /* ISO protocols */
FreeBSD provides some packet routing facilities. The kernel maintains a routing information database, which is used in selecting the appropriate network interface when transmitting packets.
A user process (or possibly multiple co-operating processes) maintains this database by sending messages over a special kind of socket. This supplants fixed size ioctl(2) used in earlier releases.
This facility is described in route(4).
Each network interface in a system corresponds to a path through which messages may be sent and received. A network interface usually has a hardware device associated with it, though certain interfaces such as the loopback interface, lo(4), do not.
The following ioctl(2) calls may be
used to manipulate network interfaces. The
ioctl() is
made on a socket (typically of type SOCK_DGRAM) in
the desired domain. Most of the requests supported in earlier releases take
an ifreq structure as its parameter. This structure
has the form
struct ifreq {
#define IFNAMSIZ 16
char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
struct ifreq_buffer ifru_buffer;
short ifru_flags[2];
short ifru_index;
int ifru_metric;
int ifru_mtu;
int ifru_phys;
int ifru_media;
caddr_t ifru_data;
int ifru_cap[2];
} ifr_ifru;
#define ifr_addr ifr_ifru.ifru_addr /* address */
#define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
#define ifr_buffer ifr_ifru.ifru_buffer /* user supplied buffer with its length */
#define ifr_flags ifr_ifru.ifru_flags[0] /* flags (low 16 bits) */
#define ifr_flagshigh ifr_ifru.ifru_flags[1] /* flags (high 16 bits) */
#define ifr_metric ifr_ifru.ifru_metric /* metric */
#define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
#define ifr_phys ifr_ifru.ifru_phys /* physical wire */
#define ifr_media ifr_ifru.ifru_media /* physical media */
#define ifr_data ifr_ifru.ifru_data /* for use by interface */
#define ifr_reqcap ifr_ifru.ifru_cap[0] /* requested capabilities */
#define ifr_curcap ifr_ifru.ifru_cap[1] /* current capabilities */
#define ifr_index ifr_ifru.ifru_index /* interface index */
};
Ioctl()
requests to obtain addresses and requests both to set and retrieve other
data are still fully supported and use the ifreq
structure:
SIOCGIFADDRSIOCGIFDSTADDRSIOCGIFBRDADDRSIOCSIFCAPSIOCGIFCAPSIOCGIFDESCRSIOCSIFDESCRSIOCSIFFLAGSSIOCGIFFLAGSSIOCSIFMETRICSIOCGIFMETRICSIOCIFCREATESIOCIFDESTROYThere are two requests that make use of a new structure:
SIOCAIFADDRioctl()
identifier itself to include the total size, as described in
ioctl().SIOCDIFADDRSIOCGIFCONFSIOCIFGCLONERSIFNAMSIZ sized strings that can be fit
in the buffer pointed to by ifcr_buffer. On return,
ifcr_total will be set to the number of clonable
interfaces and the buffer pointed to by ifcr_buffer
will be filled with the names of clonable interfaces aligned on
IFNAMSIZ boundaries./*
* Structure used in SIOCAIFADDR request.
*/
struct ifaliasreq {
char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
struct sockaddr ifra_addr;
struct sockaddr ifra_broadaddr;
struct sockaddr ifra_mask;
};
/*
* Structure used in SIOCGIFCONF request.
* Used to retrieve interface configuration
* for machine (useful for programs which
* must know all networks accessible).
*/
struct ifconf {
int ifc_len; /* size of associated buffer */
union {
caddr_t ifcu_buf;
struct ifreq *ifcu_req;
} ifc_ifcu;
#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
#define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
};
/* Structure used in SIOCIFGCLONERS request. */
struct if_clonereq {
int ifcr_total; /* total cloners (out) */
int ifcr_count; /* room for this many in user buffer */
char *ifcr_buffer; /* buffer for cloner names */
};
/* Structure used in SIOCGIFDESCR and SIOCSIFDESCR requests */
struct ifreq_buffer {
size_t length; /* length of the buffer */
void *buffer; /* pointer to userland space buffer */
};
ioctl(2), socket(2), intro(4), config(8), routed(8), ifnet(9)
The netintro manual appeared in
4.3BSD-Tahoe.
| January 26, 2012 | Debian |